When someone says he/she has no appetite does it mean that he/she cannot eat any food at all, as he is not hungry? Or does it also mean that he doesn't feel like eating although he can eat a little food if he/she wants to?

If someone says "I have no appetite." it means that person is not hungry and hasn't been hungry lately. Example: "After my surgery I had no appetite." This means that in general this person didn't feel like eating. I hope this helps!